Lamps of the type to which the present invention relate may be incandescent lamps, usually halogen incandescent lamps, having a quartz-glass bulb; the invention is equally applicable to high-pressure discharge lamps with discharge vessels made of quartz glass. The lamp bulb, or the discharge vessel, respectively, are closed and sealed by metal foils, typically molybdenum foils, which are melt-sealed in one or two portions of the bulb. Electrical energy is supplied to the electrodes through these metal foils. Externally extending connection leads, typically pins or wires, are welded to the metal foils and pass through the outer ends of the melt seals.
High-power halogen incandescent lamps, as well as high-pressure discharge lamps, in operation, generate high temperatures. The metal foils, melt-sealed to the bulb or discharge vessel, are then also subjected to high temperatures. With these high temperatures, particularly weld connections between the metal foils and the externally extending current supply leads are subject to oxidation which may become high under the high temperature operating conditions.
The lamp parts which are subject to high temperatures are frequently surrounded by an external envelope or vessel. Thus, the actual light source, that is the discharge vessel, is located within the outer envelope. The envelope can be evacuated or filled with an inert gas.
Enhanced cooling has previously been suggested with respect to highly loaded halogen incandescent lamps, for example of the type described in the referenced European Application 184,867, Mewissen. The lamp is a double-ended lamp which has two pinch seals at respective ends. The pinch seals are kept at a lower temperature by a metal envelope, which surrounds the pinch seal with space between. The base is filled with a heat-conducting mass, such as steel wool or other metal fibers. This cooling, thus, surrounds the pinch seals and hence the melt-sealed connecting foils.
Surrounding the pinch seals with an outer metal casing, filled with metallic fibers or filaments, or providing an outer envelope, substantially increases the overall size of the lamp. This increase in size reduces the applicability of the lamp for numerous uses.